Corn populations and deficit irrigation in Western Nebraska
click image to zoomGary HergertFigure 1. The field on the left in this early July 2012 photo received 0.5 inch of water earlier and then the remaining 4.5 inches over the next five weeks for a total of 5 inches. Corn in this trial yielded 118 bu/ac at 16,000 population and 125 bu/ac at 24,000 population. The area on the right had received 3.5 inches of the 15 inches it would receive by this time and yielded 200 bu/ac, even in a very dry year. Many producers in the Nebraska Panhandle will be faced with an uncertain water supply this coming year. Surface irrigators are watching snow reports in the Rockies and won’t know their allocations until spring. Many producers in ground water management areas may be nearing or at the end of an allocation period and may have less than their full allocation. With seed corn approaching $4 per 1,000 seeds, producers are questioning what populations they should plant if they face limited water.
The quandary for most producers is that they have seen continually increasing corn yields with adequate water and they have continued to push populations higher as newer hybrids withstand crowding. When you face an uncertain water supply and cannot predict the weather, you need to decide the upside and downside of your decision. If you know you will have less water, how low should your populations be? If you have limited irrigation water but it’s a wetter year, how much yield will you lose with the lower population? If you have a drier year and have a higher population, will it hurt your yield? How much? We attempted to provide research data to answer those questions.
Western Nebraska Deficit Irrigation Research
Deficit irrigation experiments in a no-till winter wheat-corn-dry bean-spring canola rotation have been conducted at Scottsbluff since 2005. The soil is a Tripp, very fine sandy loam with plant available water of 1.5 inches per foot. The primary objective of this experiment was to determine yields from deficit-irrigated corn, winter wheat, dry beans, and canola grown in a no-till cropping system versus full irrigation.
Each phase of the rotation is present each year under a linear move sprinkler irrigation system and the same irrigation level is repeated over time, so low water levels are low year after year. The irrigation levels for the crops are 4, 8 and 12 inches for dry beans, canola and wheat and 5, 10 or 15 inches for corn. The highest irrigation level was designed to be near the long-term average non-ET limiting irrigation. The irrigation levels were not set up as a percentage of ET, rather they were set to correspond to a set allocation a farmer might have. With limited water they would put on normal irrigation, but over a much shorter time period. Repeating the research over years was intended to incorporate real-world temporal variability.